1. Field of the Invention
This invention relates to electrical switch assemblies and, more particularly, to a two-link, trip-free mechanism especially useful in a high-voltage circuit breaker.
2. Prior Art
Circuit breakers generally are well known in the art and are used with a wide range of voltage levels. Circuit breakers are also used in high and ultra high voltage circuits, having voltages for example on the order of 25,000 volts, as part of the protective and safety equipment for a circuit. For use with these types of circuits, it is essential that the circuit breaker itself be trip-free in any operating position.
Trip-free means that, whether the circuit breaker is free to be tripped, or have its contacts opened, in any operating configuration of the breaker. Tripping can occur when the breaker is in its contacts-closed configuration and even during the switch-closing sequence for the switch. Either the protective and safety equipment for the circuit or an operator must be able to open the contacts at any instant and override the switch-closing sequence, if necessary, causing the circuit breaker to immediately trip open and interrupt the circuit.
In order to achieve the objective of having a circuit breaker be trip-free, a typical design for a circuit breaker mechanism utilizes several links interconnected together to move the switch contacts of the circuit breaker to their open or closed positions.
While it is highly desired in this field to provide circuit breaker mechanisms which are able to perform in a trip-free manner, the typical prior-art link arrangement for circuit breaker mechanisms are relatively complicated, requiring at least three links. Such a prior-art three-link arrangement is disclosed in U.S. Pat. No. 4,791,250, granted Dec. 13, 1988.
FIG. 1A and FIG. 1B schematically illustrate another prior-art three-link circuit breaker mechanism assembly 10. FIG. 1A shows the three-link mechanism in a tripped, open-contact position. FIG. 1B shows the three-link mechanism in a non-tripped, closed-contact position. The circuit breaker mechanism includes a conventional high-voltage electrical switch having a fixed contact 12 and a movable contact 14, both of which are adapted for use in a high voltage circuit. The assembly 10 includes a three-link arrangement consisting of links L1, L2 and L3. Link L3 is mounted for pivotal movement by a suitable rotatable, or revolute, joint 22, which is mounted in a fixed position as indicated in the drawing. The link L3 is connected at one end to the movable switch contact 14 by another revolute joint 26. The other end of the link 20 is connected to one end of a connecting link L2 by a revolute joint 28. The opposite end of the connecting link L2 is coupled to link L1 by another joint arrangement, which includes a roller 30 mounted to the end of the connecting link L2. The roller 30 is constrained to stay within a slot 32 as it contacts a cam end 34 of the link L1. Latch 36 prevents slot 32 from moving rightwardly, therefore maintaining the contact between roller 30 and cam end 34 of link L1. Latch 36 is the trip latch, while latch 44 is the closing latch, which prevents L1 from rotating. Link L1 is supported at its other end by a revolute fixed joint 38, which is mounted to a fixed support 40.
FIG. 1A shows the other prior-art, three-link mechanism with its switch contacts in an open position. Link L1 has a downward force, as indicated by FA, exerted on it by a spring 42. The link L1 is restrained from movement caused by the force FA by a releasable latch mechanism, as indicated by reference numeral 44. Force FA, when released, pivots the link 16 in a clockwise direction as indicated by arrow 45 in FIG. 1B. The force FA is coupled through the connecting link L2 to pivot the link L3 and close the switch contacts 12,14.
FIG. 1B shows the other prior-art three-link mechanism with its switch contacts in a closed position. Link L3 has a switch-opening upward force, as indicated by FB, exerted on it. This force FB is provided by a spring arrangement 46. The force FB, when released causes the switch contacts 12, 14 to be in an open position.
This other three-link arrangement provides a trip-free capability by permitting the connection as provided by the revolute joint using roller 30 between links L1 and L3 to be defeated. By freeing latch 36, the connection between link L1 and connecting link L2 is broken. The link L3 is rotated counterclockwise by the force FB of the spring arrangement 46, which results in the opening of the switch contacts 12, 14.
The foregoing description of a prior art type of circuit breaker utilizes three links to provide a trip-free, immediate override capability to the circuit breaker mechanism 10. This permits the contacts to be opened at any time during a switch-closing operation of the circuit breaker. It is to be understood that only certain components of the overall circuit breaker pertinent to the present discussion have been illustrated and that other components have been omitted for clarity.
While this particular trip-free design appears to function in a satisfactory manner, it does require the use of three links, which makes it a relatively complicated device from a structural standpoint. Nevertheless, the applicant is not aware of any heretofore available link-type of circuit breaker which does not utilize at least three links in order to provide the desired trip-free, override capabilities. Consequently, a need exists for a less complex, two-link circuit breaker.